The Elder Son part was the point of the story.

Luke 15:19-32

Many times we hear messages about the prodigal son that don't even include the part about the elder son. How unfortunate! Jesus was answering a criticism from the religious leaders about why he was receiving sinners and eating with them. The lost sheep, coin, and son all symbolized the lost condition of the people he was trying to reach and the value they had to him. But it took the part about the elder son to expose the motive of these religious leaders and their misunderstanding of the heart of God.